Electrical signal transmission system



June 1949- c. DE VIRIENDT El AL 2,474,234

ELECTRICAL SIGNAL TRANSMISSION SYSTEM Filed April 1, 1943 Patented June 28, 1949 ELECTRICAL SIGNAL TRANSMISSION SYSTEM Charles de Vriendt and Lucien A. B. Cabes, Antwerp, Belgium,

assignors to International StandardElectric Corporation, N ew York, N. Y.,

a corporation of Delaware Application April 1, 1943, SerialNo. 481,511 In theNetherlands June 21, 1941 Section '1,Public Law 690, August 8, 1946 Patent expires June21, 1961 12 Claims. 1

The invention relates to signal transmission systems and more particularly to pulse-receiving circuits.

'Heretofore, .in zmodulated carrier wave pulsereceiving circuits, it was .the vpractice, either to impress 'the rectified modulated carrier wave, through an appropriate combination of filter and transformer, directly on a steppingrelay, or to apply the carrier wave by means of a suitable transformer to the grid of a hot-cathode vacuumtubeyin which thestepping relay was inserted in "the plate circuit.

80th these'methods-have however certain disadvantages and the object of the present invention'is generally to improve and simplify modulated carrier pulse-receiving circuits.

The invention will now be "described with the aid-of "the-accompanying drawings ofwhich Fig. 1 shows a schematic "circuit arrangement according to "thepres'ent invention, whiie'Fig. 2 shows a modification thereof.

In .Fig. '1 "IMP designates an impulse sender, which may be the dial of a telephone apparatus, or a mechanical impulse machine, or any other similar appliance. Relay Sr is the stepping relay at the sending end, which connects one of the different frequencies f1 and f2 to the signalling wire.

At the receiving end there are two filters two cold-cathode tubes, two controlling .relays ,and some auxiliary apparatus.

One filter, consisting of condenser C1 and inductance S is tuned in such a way that resonance occurs with frequency 3h.

The other =.fi1ter consistsofrcondenser Czand the primary winding of transformer T, which winding islshunted by condenser 'C3. The second filter is tuned :insuch a way, that resonance occurs with frequency .fz.

The cold-cathode 'tubes referred to in this invention are of the well-known .type, which :requires .a specific control "gap breakdown potential Va: .inaorder to ionize the control gap between the two electrodes 'ei and -62, whereas a substantially higher main gap breakdown potential v 'is required to'ionize this main gap between the anode A and each of the 'two electrodes er and 22.

-Once the control gap has been ionized, 'however, a 'substaining potential'Vz, which may be considerably lower than V ,.issuiiicient to maintain a current in themaingap.

It will 'be seenflfrom Fig. 1 that the anode .of

tube-L1 is connected in series whilerelay'Ar while the anode of tube L2 is'connected inseries-with relay Am. The electrodes e2 are connected "to the negative sides of a potentiometer P, which is connected in parallel to a battery of volts. while the-electrodes e1 (thecontrolelectrodes) are connected toza biasing potentialon-the potentiometer, which is smaller-thanthe control gap breakdown voltage required to ionise the control @gap.

The twolcontrolling relays An and -AT2='001ilS10l the two cold-cathode tubes in a manner as will be:described.below. Relay -A1'1 is the actual tube control relay, whereas "relay ATz is the sig-nalreproducing relay.

The arrangement shown in :Fig. 1 functions-in the following manner.

When impulsing is about to start, the controlling :circuit at the sending end connects a potential of frequency f1 to the signalling wire via the back contact of relay Sr. This potential causes a circuit to flow through :filter -C1S1, which is tuned to the frequency f1, thereby increasing the potential on the control-electrode =.e1 of tube L1, to such an extent, that the control-gap breakdown voltage is reached. The control gap is consequently ionised. :At this moment the anode circuit-0f tube L1 is still open at the right front contact of relay :Arz, so that nothing further happens.

.As soon as the first impulse starts, :in other words, as soon as the impulse sender IMP connects aground to relay Sr for the first time, this relay operates and connects a potential of frequency f2 (instead of ii) to the signalling wire. This potential causes a current to flow through the second filter C2-T, which is tuned to the frequency f2, thereby inducing in the secondary winding of transformer T a potential, which is added to the biasing potential of electrode 01 0f tube L2, and which increases this potential 'to such an extent that the control gap breakdown voltage is reached. The control gap is "consequently ionised, resulting in the immediate ionisation of the maingap and the operationof relay Am in the anode circuit of the tube L2. When operated this relay closes the receiving end signal circuit via its left front contact and prepares the anode circuit of relay ATI over its right front contact.

To this may be added that at the moment the armature of relay Sr leaves its back contact, the potential of frequency f1 is removed from the signalling wire with the result that the "tube in is extinguished; its anode circuit :bein'g already open.

When the first impulse is over, i. e. when the impulse sender IMP removes the ground from relay Sr, this relay releases, thus removing the potential of frequency 2 from the signalling wire. Tube L2 remains, however, ionised, after the armature of relay Sr leaves its front contact, because its anode circuit remains closed. As soon as the armature of relay Sr closes its back contact, a potential of frequency fl is connected to the signalling wire. This potential causes the ionisation of the control gap of tube L1 as explained above and at this moment also the main gap of tube Li becomes ionised, the anode circuit through relay ATl being closed via right front contact of relay Ara.

Relay Ari therefore operates and as soon the armature leaves the back contact, the anode circuit of tube L2 is opened, whereupon this tube extinguishes. As a consequence relay Ar2 releases, opening the receiving end signal circuit and interrupting the anode circuit of tube L1, thus causing the release of relay A11.

The control gap of tube L1 remains ionised due to the presence of a potential of frequency ii on the signalling wire, as explained above.

A non-inductive resistance T4 is connected in parallel to the winding of relay Arm for the purpose of discharging the relay as soon as its operating circuit is opened. This is desirable in order to speed up the de-ionisation of tube L1.

One impulse has now been transmitted and the circuits are in the same condition as at the moment the impulsing started.

All subsequent impulses are transmitted in exactly the same manner.

From the above description it follows that the invention as illustrated by Fig. 1 provides a very sensitive signal transmission, suitable for instance for application in local impulse transmitting circuits or similar circuits for transmission over long distances.

The invention is based on the principle that each pulse or signal comprises two components of different frequencies, which are separated at the receiving end by adequate filters, each of the two different components being utilised to ionize alternately a cold-cathode tube.

In Fig. 2 an alternative arrangement is shown, which differs from Fig. 1 in the manner in which the anode circuits of the tubes have been designed. In Fig. 2 the anode control relay has been replaced by a condenser C4, while the signal relay Ara has been connected in series with both anodes.

The scheme functions as follows:

When impulsing is about to start, a frequency ii is connected to a signalling wire and, as previously explained, tube L1 is ionised, an anode current now flowing through the resistance 1'3. Since the sustaining voltage of tube L1 is about 75 volts, the potential at point a will be about 55 volts with respect to point 0. Condenser 04 will consequently be charged in a direction indicated by and in full lines, since point 2) is of the same potential as point 0.

As soon as the impulsing starts, relay S1 operates and frequency f2 is connected to the signalling wire, causing the ionisation of tube L2 and the operation of the stepping relay A13. The potential at point 2) will now fall to 55 v. with respect to point 0, with the result that condenser C4 will discharge. This discharge current will cause an additional, temporary Voltage drop across resistance 13, which will produce a lowering of the potential of point a with respect to point 0. Since the total voltage across the main gap circuit is volts and since the voltage drop across resistance 1-3 is greater than 55 volts, the available voltage between the main gap of the tube will be less than '75 volts (sustaining voltage) with the result that tube L1 will extinguish.

At the moment the current through 1'3 disappears, point a will attain the same potential as point 0. Condenser C4 will now be charged in opposite direction, indicated by and in dotted lines.

When the first impulse is over, relay Sr releases and frequency I1 is again connected to the signalling wire. The tube L1 will then become ionised and the potential of point a will again drop to about 55 volts with respect to point 0. Condenser C4 will now start to discharge and the discharge current causes an additional voltage drop in relay Ara, which results in the extinction of tube L2 and the release of relay Ara.

Point 1) will then attain the same potential as point 0 and the original conditions will again be re-established.

Each impulse is reproduced in exactly the same way as described above.

What is claimed is:

1. An electrical signal transmission system comprising a transmission line, signal transmission apparatus connected to one terminal of said line, said signal transmission apparatus comprising means to transmit alternate impulses of two different frequencies, means connected to the opposite end of said line for receiving said impulses said receiving means comprising a pair of circuits, means in one circuit responsive to energy of one of said frequencies applied thereto to register the beginning of an impulse and means in the other of said circuits responsive to energy of the other oi said frequencies applied thereto to register the end of an impulse and relay means associated with said receiving means jointly controlled by both of said circuits for retransmitting signals measured by the two frequencies of each impulse received.

2. An electrical signal transmission system according to claim 1 in which said signal transmitting device comprises a substation dial, a relay controlled thereby, contact means for said relay including a tongue, front and back contacts cooperating therewith, a source of a first signalling frequency potential connected to said back contact, a source of a different frequency potentialconnected to said front contact, said tongue being connected to said transmission line.

3. An electrical transmission system according to claim 1 in which said receiving means comprises electrical filter means for segregating the two currents of different frequencies.

4. An electrical transmission system according to claim 1 in which said receiving means comprises electrical filter means for segregating the two currents of different frequencies, a pair of cold cathode tubes, circuits connecting the control electrodes of the respective tubes to said filter means so that each tube is operated by a separate frequency.

5. An electrical transmission system according to claim 1 in which said receiving means comprises electrical filter means for segregating the two currents of different frequencies, a pair of cold cathode tubes, circuits connecting the control electrodes of the respective tubes to said filter means so that each tube is operated by a separate frequency, a common source of biasing potential for each tube of such value that each signal component received will cause the operation of the corresponding tube.

6. An electrical transmission system according to claim 1 in which said receiving means comprises electrical filter means for segregating the two frequency components of the respective impulses a pair of cold cathode tubes, circuits connecting the control electrodes of the respective tubes to said filter means so that each tube is operated by a separate frequency of the received impulses, a pair of relays, of which one is connected in the anode circuit of each of said tubes whereby the relays operate on the operation of the corresponding tube, and circuits controlled from the contacts of the respective relays for controlling the extinguishing of said tubes.

7. An electrical signal transmission system comprising a transmission line, signal transmission apparatus connected to said line, said apparatus comprising means to transmit alternate impulses of two different frequencies, means connected to the opposite end of said line for receiving said impulses, said receiving means comprising electrical filter means, for segregating the frequencies of the respective impulses, a pair of cold cathode tubes, a circuit connecting the control electrode of each of said tubes to said filter means so that each tube responds to the application of energy of a different frequency of the respective impulses, a relay connected in the anode circuit of each tube, the relay associated with the first of said tubes being connected in an operating circuit including the back contact of the other relay, while the operating circuit of the latter relay includes the front contacts of the relay associated with the first of said tubes, the arrangement being such that the first of said tubes and the relay associated therewith operates an impulse of the first frequency and closes at its front contacts an operating circuit for the other relay which operates when the second of said tubes is operated by receipt of impulse the second frequency thereby at its back contact opening the circuit for the first of said tubes and the associated relay, the latter on releasing opening the operating circuit for the second tube and the associated relay, and further contact means operated by the relay associated with the first of said tubes for transmitting impulses.

8. An electrical signal transmission system comprising a transmission line, signal transmission apparatus connected thereto, said apparatus comprising means to transmit alternate impulses of two different frequencies, one of said frequencies indicating the beginning of an impulse and the other the end thereof, receiving means connected to said line comprising electric filter means for segregating said respective frequencies, a pair of electronic tubes operatively connected to said filter means whereby one tube responds to application of energy of an impulse of one frequency and the other tube to application of energy of an impulse of the other frequency, relay means connected to the output circuit of said tubes so as to respond to the operation thereof, and means controlled by said relay means for retransmitting impulses.

9. A signal transmission system according to claim 8 in which said relay means is a single relay.

10. A signal transmission system according to claim 8 in which said relay means comprises a single neutral relay.

11. A signal transmission system according to claim 8 in which said relay means comprises a single neutral relay and in which condenser means connected across the output of said electronic tubes is used to control said relay means.

12. A signal transmission system according to claim 8 in which said relay means comprises a single neutral relay and in which a condenser is connected between the output electrodes of said electronic tubes, said condenser being used to control said relay means.

CHARLES DE VRIENDT. LUCIEN A. B. CABES.

REFERENCES CITED The following referenrces are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,045,735 Taylor June 30, 1936 

